1 Field of the Invention
An object of the present invention is a method for the fabrication of aluminium electrolytic capacitors with solid electrolyte or gelled liquid electrolyte, as well as capacitors obtained thereby.
2. Description of the Prior Art
Electrolytic capacitors are used above all because of their high capacity in a restricted volume. At present, there are three groups of low C.times.V product electrolytic capacitors on the market. There are aluminium capacitors with liquid electrolyte: the anode is made of aluminium and the cathode is an electrolytic liquid. There are also tantalum capacitors with solid electrolyte: the anode is made of tantalum and the cathode is a solid semiconductor electrolyte. Finally, there are aluminium capacitors with solid electrolyte: the anode is made of aluminium and the cathode is a solid semiconductor electrolyte.
The last-named group of electrolytic capacitors has recently seen undoubted development. The firm, Philips, has developed several ranges of aluminium electrolytic capacitors with solid electrolyte. The anode is made with a rolled or folded foil. The manufacturing method, using a foil anode, comprises the following steps:
the punching of an aluminium foil; PA1 the etching of the foil; PA1 folding of the etched aluminium foil in the case of radial capacitors, or rolling it up in the case of axial capacitors; PA1 anodization of the foil to form a thin alumina layer; PA1 formation of the solid electrolyte (manganese dioxide) by pyrolysis; PA1 positioning of the cathode. PA1 the obtaining of a connections strip made of aluminium, having anode contacts, PA1 the fixing, to the anode contacts, of aluminium blocks either by sintering or by the spraying of molten aluminium, PA1 the anodization of the aluminium blocks; PA1 the impregnation of the blocks with said electrolyte; PA1 the positioning of the cathode contacts.
The method used to fabricate these capacitors is fairly complicated. It comprises a one-by-one folding operation in the case of radial capacitors or one-by-one rolling in the case of axial capacitors. The solid electrolyte forming stage is the most difficult one. Several cycles of pyrolysis (four in principle) are needed, and these cycles should occur under well-defined conditions of temperature and duration. These operations are very difficult to control. For, the basic product used is a very aggressive solution of manganese nitrate. The conversion into manganese dioxide should be very fast. A post-forming operation is needed to repair the alumina layer damaged by the nitrate.
To avoid at least a part of these difficult steps, the invention proposes a fabrication method which can be used to obtain aluminium electrolytic capacitors with solid or gelled liquid electrolyte, using aluminium blocks generated on the anode contacts either by sintering or by the spraying of molten metal. The invention also enables the use of an organic electrolyte instead of manganese dioxide.